1. Field of the Invention
The present invention relates to a stripper assembly for an injection molding machine.
2. Summary of the Prior Art
Injection molded products are produced in a mold shoe of an injection molding machine. Such a mold shoe comprises an assembly of inserts that cooperate to form a complete mold cavity. A mold shoe of an injection molding machine is normally considered as being made of two halves, namely a hot and a cold half. Typically, the cold half is secured to a moving platen of the injection molding machine, whereas the hot half is secured to a stationary platen. The mold halves are operable between a mold open and a mold closed position by reciprocation of the moving platen. Very broadly speaking, when the mold halves are in their closed position, a mold cavity is formed by a recess in the hot half forming the outside geometry and a core on the cold half forming the inside geometry. The recess and the core generally comprise a number of individual inserts.
After injecting plastic melt into the mold cavity and allowing it to achieve sufficient solidification to withstand part ejection forces without undue deformation, the mold shoe halves are opened. The newly formed products are thereby released from the hot half inserts while still being retained on the cold half inserts. The release of the completed products from the cold half inserts is performed by a stripper assembly mounted on the cold half of the mold shoe. Indeed, the cold half generally comprises a core plate assembly having a subset of the cold half inserts mounted thereon and a stripper assembly for stripping the completed products off the cold half inserts. Such a stripper assembly is connected to actuation means for operating the stripper assembly between a back and a forward position with respect to the core plate assembly. The stripper assembly further comprises at least one slide pair. While operating the stripper assembly between the back and forward position, a release mechanism operates the slides of the slide pairs between an open and a closed position, wherein corresponding slides within a pair diverge and converge respectively while remaining mutually parallel.
The cold half inserts comprise core, neck ring and lock ring inserts. The core and lock ring inserts are secured on a face of the core plate assembly, and corresponding neck ring halves are secured on opposing slides. The neck ring inserts mounted on the slides retain the product on the cold half of the mold shoe as the cold half is separated from the hot half. Once the products have sufficiently cooled, they can be released from the cold half. In order to do so, the stripper assembly is moved from its back to its forward position, thereby pushing the product over the core insert. As the stripper assembly gets close to its forward position, the slides are operated towards their open position by means of the release mechanism. The slides and the neck ring halves mounted thereon diverge and release the completed product Once the parts have been released, the stripper assembly is moved from its forward to its back position and the sides are operated to their closed position by means of the release mechanism.
A typical release mechanism uses cams to establish a defined relationship between the position of the stripper assembly in its stroke relative to the core plate assembly, and the separation position between slides in a corresponding pair.
One typical approach to release mechanism design uses cams that have profiled surfaces that bear directly against compatible slide surfaces, wherein the profile of the cams control the positional relationship of the slides. Such a release mechanism is however not ideal as each slide pair requires its own pair of opening cams.
Another typical approach uses a simplified design of the release mechanism, linking together of all of the slides going in one direction. Such a release mechanism e.g. has the slides opening to the left connected by means of a connecting bar and the slides opening to the right connected by means of another connecting bar. Each linked set includes a cam follower mounted to either a connecting bar or to a slide and comprises a cam follower moveable within a cam to operate the slide pairs between their open and closed positions. The main disadvantage of this release mechanism is an inefficient use of space that results from connecting all of the slides that are to move in the same direction to a common connecting bar. Specifically, practical design considerations dictate that the way the slides and connecting bar are connected cannot be symmetrical about the middle of the mold, and therefore may create spatial restrictions (e.g. interference with a tiebar) in one corner of the mold that are not an issue in another. A further disadvantage is that the two halves of the release mechanism are independent, and hence require separate cams or cam profiles.
Another release mechanism is disclosed in U.S. Pat. No. 4,521,177. This release mechanism comprises a guide plate mounted a core plate assembly. The slides are slideably arranged in the guide plate. A first adjustment bar is arranged between the core plate assembly and a first slide, whereas a second adjustment bar is arranged between the core plate assembly and a second slide. Both adjustment bars run at right angles to the direction of displacement of the slides. They comprise grooves extending at an acute angle to the longitudinal direction of the adjustment bars for receiving thrust pins connected to the slides. The grooves of the two adjustment bars are inclined in opposite directions so as to operate the slides in opposite directions as the adjustment bars are displaced. Both adjustment bars are connected via a yoke to actuation means. The problem with this release mechanism is that due to the high number of elements in the actuator coupling, there is a risk that the slides do not open simultaneously. This can then cause the molded product not to be released properly. Furthermore, due to the adjustment bars, the design of the stripper assembly becomes rather cumbersome.
The object of the present invention is to provide a stripper assembly, which has a simple release mechanism while at the same time making the stripper assembly more compact.
In order to overcome the abovementioned problems, the present invention proposes a stripper assembly for an injection molding machine comprising at least one slide pair having a first slide and a second slide and actuation means operatively coupled to said first slide for moving the first slide in a first direction. According to an important aspect of the invention, the stripper assembly further comprises transmission means operatively coupled to said first slide and said second slide for transforming the movement of the first slide in the first direction in a movement of the second slide in a second direction, the second direction being opposite to the first direction. The release mechanism of this stripper assembly, i.e. the actuation means and the connection means is a very simple design and it allows for a very compact design of the stripper assembly. Actuating means are provided for the first slide only. The second slide is coupled to the first slide by the transmission means. By using transmission means capable of transforming the movement of the first slide in a first direction in a movement of the second slide in the opposite direction, there is no need to supply actuation means for the second slide. A further advantage is that the movement of both slides is always synchronized. This is because, due to the transmission means, the movement of the second slides depends directly on the movement of the first slide. If the movement of the slides is not synchronized, the molded product may not be released properly, causing a production stoppage in order to avoid damage to any parts.
According to a preferred embodiment, the stripper assembly has a set of slide pairs with at least one first connecting bar for connecting the first slides and at least one second connecting bar for connecting the second slides. By connecting corresponding slides together, several slide pairs can be operated simultaneously by one and the same actuation means. Actuating means are provided for the first connecting bar only. The second connecting bar is coupled to the first connecting bar by the transmission means. By using transmission means capable of transforming the movement of the first connecting bar in a first direction in a movement of the second connecting bar in the opposite direction, there is no need to supply actuation means for the second connecting bar.
According to another preferred embodiment, the stripper assembly has a first set of slide pairs and a second set of slide pairs, wherein each pair comprises at least one first connecting bar for connecting the first slides and at least one second connecting bar for connecting the second slides. Actuating means are provided for each first connecting bar only. The second connecting bars are coupled to the first connecting bars by the transmission means. Due to the transmission means there is no need to supply actuation means for the second connecting bars.
The first slides of the first set and the first slides of the second set are advantageously operated in opposite directions. This is of particular advantage as interference between the tiebars and the connection bars can be greatly reduced. Indeed, with previously known stripper assembly assemblies, the number of slide pairs was limited due to the fact that, as the slide pairs diverged, one of the connecting bars would hit the tiebar. With the stripper assembly according to the invention, this problem is solved in that the connecting bar that would hit the tiebar is replaced by two connecting bars moving in opposite directions. Indeed, the first connecting bars of the first and second set are both moved away from the tiebar. It is hence possible to increase the number of slide pairs on the stripper assembly, and also the number of inserts in the mold shoe within a given tiebar spacing. This then allows an important increase in production volume with a minimum of alterations to the system.
The first and second connecting bars are advantageously connected to the first and second slides at first end portions thereof, and preferably also at second end portions thereof. The release mechanism is thereby confined to the edges of the stripping assembly. The number of products produced per slide pair is hence not reduced by the release mechanism.
The transmission means preferably couple the at least one first connecting bar to the at least one second connecting bar.
According to first embodiment the transmission means comprises a pivoting lever pivotably mounted between the first and second slides, a first end of the pivoting lever being coupled to the first slide and a second end of the pivoting lever being coupled to the second slide. Such a lever provides a very simple means for transmitting movement of the first slide in a first direction to a movement of the second slide in the opposite direction.
According to second embodiment the transmission means comprises a first toothed face coupled to the first slide; a second toothed face coupled to the second slide, the first and second toothed faces facing each other; and a gearwheel engaging the first and second toothed faces. Such a gear mechanism also provides a very simple means for transmitting movement of the first slide in a first direction to a movement of the second slide in the opposite direction.
The actuation means is preferably mounted on the at least one first connecting bar. The actuation means preferably comprises a cam follower connected to the first slide, and a cam in which the cam follower is movable for moving the first slide in the first direction. Such actuation means are of very simple design and allow the release mechanism to be activated by simply operating the stripper assembly between its backward and forward positions. No actuator is needed for operating the release mechanism. This thus also contributes to the compactness of the design. The release mechanism is automatically interlocked with the stripper assembly motion ensuring no risk of misaligned or mistimed slide motion which could cause damage.
The invention also concerns an injection molding machine having a stripper assembly as described hereabove.